Add web documentation + installation instructions (#19342)
### Description
Updated docs section with information on installation and building.
Live previews of modified pages:
* [Installation
table](https://carzh.github.io/onnxruntime/getting-started) -- under the
Optimize Training tab
* [Build for
training](https://carzh.github.io/onnxruntime/docs/build/training.html)
* [Getting started with
web](https://carzh.github.io/onnxruntime/docs/get-started/with-web.html)
-- added link to E2E demo code
* [Install for on-device
training](https://carzh.github.io/onnxruntime/docs/install/#install-for-on-device-training)
* [Tutorials page for On-device
training](https://carzh.github.io/onnxruntime/docs/tutorials/on-device-training/)
-- this page looks a little odd with just the link to the E2E demo.
potential alternative of creating a separate page that links to the demo
+ mentions that a tutorial will be coming soon?
### Motivation and Context
- Updating docs with information about ORT Training for Web for 1.17
release
